In this paper, a compact spectrometer based on disordered rough surfaces for operation in the terahertz band is presented. The proposed spectrometer consists of three components, which are used for dispersion, modulation and detection respectively. The disordered rough surfaces, which are acted as the dispersion component, are modulated by the modulation component. Different scattering intensities are captured by the detection component with different extent of modulation. With a calibration measurement process, one can reconstruct the spectra of the probe terahertz beam by solving a system of simultaneous linear equations. A Tikhonov regularization approach has been implemented to improve the accuracy of the spectral reconstruction. The reported broadband, compact, high-resolution terahertz spectrometer is well suited for portable terahertz spectroscopy applications.
By using a preaggregated silver nanoparticle monolayer film and an infrared sensor card, we demonstrate a miniature spectrometer design that covers a broad wavelength range from visible to infrared with high spectral resolution. The spectral contents of an incident probe beam are reconstructed by solving a matrix equation with a smoothing simulated annealing algorithm. The proposed spectrometer offers significant advantages over current instruments that are based on Fourier transform and grating dispersion, in terms of size, resolution, spectral range, cost and reliability. The spectrometer contains three components, which are used for dispersion, frequency conversion and detection. Disordered silver nanoparticles in dispersion component reduce the fabrication complexity. An infrared sensor card in the conversion component broaden the operational spectral range of the system into visible and infrared bands. Since the CCD used in the detection component provides very large number of intensity measurements, one can reconstruct the final spectrum with high resolution. An additional feature of our algorithm for solving the matrix equation, which is suitable for reconstructing both broadband and narrowband signals, we have adopted a smoothing step based on a simulated annealing algorithm. This algorithm improve the accuracy of the spectral reconstruction.
Optical modulation of terahertz surface plasmon polaritons (THz SPPs) propagating in an intrinsic indium antimonide surface is demonstrated in this paper. The modulation is mediated by the modification of free carrier density with optical illumination. Simulation and experimental results show that a THz modulator can be realized by tuning the propagation lengths of THz SPPs, which could be controlled to be larger or shorter than the distance of two razor blades used for the coupling of the THz wave and the THz SPPs. In comparison with conventional THz modulation approaches, this method of manufacturing is simpler and the switching bandwidth is wider. The maximum modulation frequency of the modulators is anticipated to be above gigahertz, thus leading to the possibility of communication applications using the THz baseband.
We investigate the influence of profile of one-dimensional (1D) Ag gratings on the enhancement factor (EF) of surface-enhanced Raman scattering (SERS). An optimized duty ratio of 1D Ag grating is found, and the SERS EF is experimentally obtained on the order of ~ 104, while the finite-difference time-domain simulation shows that the SERS EF can be as high as ~ 106. We ascribe the discrepancy between the simulated and the experimental results mainly to the fluctuation of Ag grating structure, which is confirmed by the topography measurement using scanning electron microscopy and atomic force microscopy.
We have studied the harmonic generation and the effective nonlinear-optical coefficients of the quasi-periodic optical superlattice (QPOS). It has been shown that the effective nonlinear-optical coefficients in QPOS are the extension of that in periodic optical superlattice (POS). The intensities of the harmonic generation obtained by the coupled-wave equations are in good agreement with prediction by the effective nonlinear-optical coefficients.
It was found that the ferroelectric coercive field of LiNbO3, both in forward and reverse direction, vary with time after domain inversion. The existence of an internal field decaying as e-t/(tau ) is proposed, and the related coefficients are fitted.
Surface corrugations with periodic of 2 micrometers and a depth of approximately 150 nm have been fabricated in lithium tantalate (LiTaO3) monocrystal wafers. Morphologies of the corrugations were studied with an atomic force microscope. These corrugations were first produced by a single excimer laser pulse through a diffractive optical element, and the optical quality of the periodic structures is demonstrated by its characteristics as a gratings coupler in a LiTaO3 planar waveguide.